This proposal, "Alternative Photosensitization Assay in the Mouse (Photo-LLNA)," is an alternative animal test designed to identify substances with immunotoxic properties. There has evolved an industry demand and a governmental mandate to develop alternative toxicity tests that refer, reduce, or replace the use of animal models. Due to increasing concerns over the photoallergic (photosensitizing) properties of chemicals, there is an increasing need for rapid, cost-effective assays, which can predict not only sensitization, but also photosensitization. The Local Lymph Node Assay has proven to be a useful, sensitive model for detecting sensitizers. The purpose of this proposal is to demonstrate the feasibility of employing the LLNA, combined with UV irradiation, as a test system to identify potential photosensitizers or photoirritants. Few papers have been published in the literature using this model, thus this is a relatively novel application of this test system. The choice of a mouse model has several advantages over guinea pig tests, including the use of a known predictive mechanistic assay system, which is rapid, cost-effective, and minimizes pain and distress to animals. The Photo-LLNA Assay will provide a sensitive test system while; (1) complying with the Animal Welfare Act by directly addressing the 3Rs; (2) increasing the discriminating power and quality of data generated when compared to existing methods; and (3) greatly reducing the costs associated with the use of animals for photosensitization studies. PROPOSED COMMERCIAL APPLICATION: MB Research will offer the service of an alternative photosensitization assay to members of the pharmaceutical, biotech, cosmetic, and chemical industry. A survey of our clients indicates there is an increassing demand for rapid and cost-effective photosensitization tests, as well as for mechanistic-based tests, which provide both qualitative and quantitative information. In addition, we believe that flow cytometry is underutilized in the toxicity-screening field and that this technology can be used to develop other commercially viable in vivo and vitro toxicity test at our company.